Out of necessity, this will be a long post, backed by the experience of nearly fifty years watching and researching -- mostly the former PRR Middle Division, but with some other examples thrown in. If any other members could add amplifications of corrections, it would be very much welcomed and appreciated.
The Pennsylvania began listing "Arranged Freight Train Service" a long time ago. Old issues of Railway Age referred to freight moves by symbol as early as the first World War; and the earliest Employee Timetables I've seen listed most Enola-Altoona-Pittsburgh moves as M- (for Middle) 1, 2, 5, 6, etc. Not too many were listed , but I suspect operating "in sections" was more common, since traffic as a whole was more volatile. More, and faster services for markets like New York-Pitsburgh and New York-Buffalo began to appear as competition from trucking materialized after 1930.
But things really began to get complicated after World War II; the work "The Pennsy in Chicago" by the late Ed DeRouyn listed about twenty daily eastbound symbol freights originating in the Windy City around 1950. The Pennsy had at least four major yards (Harsimus Cove, Meadows, Greenville and Waverly) in northen New Jersey alone, and excess freight could be swapped between some of the schedules without the addition of a "B" or second section in a lot of cases, Still, the limitation of an M-1 Mountain type to about 75 cars meant that a lot of additional moves would be necessary from time to time, particularly when a large produce block came from the Santa Fe, Burlington. or one of the UP's granger partners,
It's also worth noting that eastbound PRR freight traffic moved mostly via Logansport, Ind. and the "PanHandle" route rather than the old "Eastern" (Ohio) Division via Crestline, which had a couple of stiff grades. Some PRR ETT's from the Fifites and Sixties showed an option of using either route for a handful of moves, and the high-priority livestock-handling FW- (for "Feed and Water")-8 opted for the passenger-heavy route via Fort Wayne, Lima and Crestline. (In a last-ditch attempt to retain livestock traffic, this service was re-symbolled NF- (for "No Feed")-4 or -6, but to no avail).
Traffic from southwestern connections at St. Louis moved on a series of freights symbolled SW-, with only one (SW-6) venturing as far east as Enola; presumably, much of the traffic could be folded into the much larger volume from Chicago somewere along the line. Lots of westbound empties were generated in the process, and these moved mostly on a series designated LCL- (later changed to PR-), and presumably headed for the Pennsy's "new" breakbulk on the north side of downtown Pittsburgh, but in reality, underutilized practically from the date of its completion. When traffic got very heavy, as in the days of the Vietnam-related 1964-66 defense build-up, "B" sections could show up on several moves, and solid extras of empties sometimes went west. And by some strange reasoning, Middle Divy maids-of-all-work M-9/10 were revived for about a year, and I saw as many as five sections on the block operator's train sheets on a few occasions.
Things began to fall apart rapidly after the Penn Central bankruptcy and the completion of toll-free Interstate 80 between Youngstown and Stroudsburg in the summer of 1970, almost all the dressed meat traffic from the Plains states disappeared within a few months, for example. An attempt to recapture wetern perishable traffic via a service symbolled AST- ("Astronaut") didn't get too far, either. The near-complete demise of passenger service finally got the PC brass thinking about cutting the Middle Divy down from three tracks (one usually signalled in both directions) to two, but this process was not started until around 1981, and completed two years later.
Rerturning to the present day, I can see from the windows of my "Tuesday-Saturday" address here in Topton along the former Reading, that a lot of high-priority traffic has found its way back onto the rails, some of it with forwarders like Clipper or perishable-oriented truckers like Stevens, and Interstate 80 doesn't seem as crowded with either perishable or "dry freight" rigs as it did in the Seventies when I dispatched for a couple of regulated truckers, Traffic coming up from the South, Southwest, and presumably, Mexico on i-81, seems to have increased, however.
PRR never operated multiple sections on its famous TrucTrains; the sales department seemed interested only in a predictable quantity of stable business. But the ETT's did list a couple of moves carrying much higher suffix numbers and operating only on weekends or "as required"; moves designated "TT-SPL" also showed up from time to time. That practice also seems to have carried over to the present, as I will occasionally catch short, unanticipated intermodal moves eastbound from Enola on the weekends.
And as we've touched on in other posts, the railroads don't seem to have much interest in improving the fluidity of their two-way-signalled double track lines via adding a third track or sidings for overtaking moves; UP's three-track stretch between Gibbon and North Platte, Neb, is about the only place where there would be room to experiment, and NYC's attempt to mix freight and the remains of the Great Steel Fleet via the use of strategically-placed "long sidings" gradually fell apart in the Sixties. And of course, everybody's "waiting for the shoe to drop" regarding PANAMAX.
And in a final observation from a varied and checkered career, I was fortunate to have spent a few months back around the "turn of the millenium" (??) holding down a daily assignment as a courier that gave me a regular opportunity to check out UP's main line between Omaha, Blair and Fremont, Neb. The prectice seemed to be to keep the time-sensitive intermodals (UP handled very few, if any solid trains of automotive or similar commtment-based freight) moving on strict schedules, while the general-service freights often spent a lot of time in sidings waiting to recrew -- especially on holiday weekends.
So while the industry has been restored to health at a pattern similar to public utilities, It seems clear that daily operations aren't quite as interesting to watch, not do they offer as much variety as when this writer was starting out -- too many years ago.
What a revoltin' development this is! (William Bendix)